This invention relates to the field of lamp starting circuits. More specifically, it relates to circuits designed for initiating operation of gaseous discharge lamps such as the sodium vapor type commonly employed for street lighting. Such lamps require high voltage starting pulses in order to initiate the ionization process. Subsequent operation of the lamps is maintained by a large ballast connected in series with the AC voltage source.
Lamp starting circuits are known in the art and see, for example, the patents discussed in the prior art statement which follows. A principal drawback of the prior art is the inability of these designs to protect the starting circuit from premature failure where the lamp or power factor capacitor fails. Under those conditions the starting circuit repeatedly fires in an effort to light the lamp and in many cases this causes overheating of the starting circuit leading to premature component failure.
Another disadvantage of the existing circuits is that in order to prevent current flow through the trigger circuit isolation components are required as, for example, the use of an inductance which has a high impedance at the pulse frequency. Also, presently available circuits do not provide means whereby a service technician can rapidly check and service a lamp which is not properly operating. Instead, the technician must check each component of the operating circuit, the starting circuit and the lamp until he determines the source of the problem. It would be desirable to provide a starting circuit which includes indicator means permitting the technician to rapidly determine the source of a lamp failure thereby to quickly affect repair or replacement.
It is accordingly an oject of the present invention to provide an improved lamp starting circuit in which the starting circuit components are not subject to premature failure in the event that the lamp or an associated component fails thereby inducing repeated starting pulses.
Another object of the invention is to provide an improved starting circuit in which current does not pass through the circuit after the starting pulse has been produced until the circuit resets itself and is ready to begin recharging.
A further object of the invention is to provide a starting circuit embodiment in which high impedance isolating components are not required to protect the circuit against the high voltage pulses produced.
A further object of the invention is to provide a starting circuit which includes indicator means permitting a technician to rapidly determine whether the starting circuit is performing satisfactorily or is defective.
Other objects and advantages of the invention will be apparent from the remaining portion of the specification.